On the first personal computers (PCs) developed by IBM, the operating system and applications executed were relatively compact, sharing about one megabyte of address space. PCs including desktop and portable laptop computers have subsequently evolved to much more sophisticated designs. Graphic operating systems and applications requiring much more memory have become common, and it is not unusual for PCs and laptop computers to be sold with 16 or more megabytes of random access memory (RAM) installed. In contrast to the increasing amount of RAM installed on PCs, portable personal information (PIM) devices have recently been introduced that include a microcomputer or microprocessor provided with only enough RAM to enable the dedicated PIM functions to be performed. PIM devices must be distinguished from personal data assistants (PDAs) that include sufficient RAM to enable small application programs specifically developed for the PDA to be executed. PIM devices provide very limited computational functions, and much of the functionality of the devices is programmed into read only memory (ROM). RAM is typically not provided on a PIM device for running application programs that are downloaded into non-volatile read/write memory. An example of a PIM device is the Timex DATA LINK wristwatch, which provides timekeeping functions and stores PIM data that are downloaded from a PC through a sensor that responds to a predefined modulation of scan lines on the PC monitor.
Data can be downloaded into a non-volatile read/write memory of a portable computing device such as a laptop computer from a conventional PC using a variety of different mediums, including: radio frequency (RF) links, infrared (IR) data links, and data cable connections. In addition to the screen modulation technique noted above, these same data transfer mediums can be employed to download data into a portable PIM device. A PC is preferably used for compiling/entering the data, since the keyboard of the PC permits more efficient data entry, the hard drive of a PC conveniently provides long term storage, and data are more easily reviewed on the PC display. Application programs are not normally downloaded to a PIM device from a PC, because the 2-4 Kbytes (or less) of RAM provided on the typical PIM device is generally considered too small for executing downloaded code.
More recently, however, a combination pager and PIM device has been developed that will receive conventional paging messages and paging objects that are used to update PIM data and other data maintained in non-volatile read/write memory in the device. The data stored in the device includes the typical PIM type of data noted above, e.g., addresses, telephone numbers, and names. However, the dual purpose paging device requires that it also be capable of executing small application programs called “applets” using the very limited amounts of RAM provided on the device, i.e., typically less than 4 Kbytes. Those familiar with programming applications for execution by a microprocessor will appreciate that with even the most careful and efficient coding, it is generally not possible to implement more than a trivial application with machine instructions that will fit into 4 Kbytes of RAM. Accordingly, a new approach was developed and is described in co-pending application entitled “APPLICATION EXECUTION ENVIRONMENT FOR A SMALL DEVICE”, Ser. No. 08/825,645, filed Apr. 3, 1997, now U.S. Pat. No. 6,226,665, issued May 21, 2001, which is hereby incorporated by reference, allows processing of larger amounts of application code in a very limited amount of RAM.
Another problem with current remote devices involves updating the information downloaded to the remote device. Commonly, the user must return to a personal computer or other downloading station in order to download a new dataset that has been updated with new information. Although a PIM device, such as the watch described above, can updated without an electrical connection between the watch and the updating computer, such a system still requires the user to return to the computer in order to receive the update. In addition, the user must download the complete dataset although only small portion may have been updated.